One disadvantage of traditional mooring is the necessity to constantly adjust the mooring lines, particularly when a ship is secured to a fixed dock. This adjustment is to account for movement of the ship in response to winds, shifting tides, the addition or removal of cargo, and the like. The combination of high tidal movements and variations in ship displacement due to loading can result in a considerable vertical movement having to be accommodated by the mooring system.
With a mooring device such as that described in the co-pending U.S. application Ser. No. 10/220,009 which is based upon New Zealand Patent application No. 501395 (which specification is incorporated herein by reference), a vacuum attachment cup assembly is fixed to the ship's hull. Mechanical means limits movement of mooring robot up and down over the full extent of the relative vertical travel. This possible movement necessitates a larger working area, with consequent complication and increased cost.
Japanese patent abstract publication no. 58206478 describes a mooring device and a method of changing the position of a vacuum cup fastening the device to the hull. When the device reaches the limits of its vertical travel the negative pressure in the vacuum cup is raised to a degree permitting the cup to slide without releasing from the hull. At its limits of travel this passive method therefore offers greatly reduced mooring forces, making the moored vessel vulnerable to failure of the mooring in adverse conditions of weather and current. The seal of the vacuum cup also suffers from abrasion when the cup slides down the hull in this manner and so to avoid regular sliding movement during operation the mooring device is provided with increased mechanical travel in the vertical direction, with consequent added complication and expense.
It is an object of the present invention to provide a mooring system and method of operating a mooring system for accommodating a large relative vertical movement of a ship when docked. It is a further objective of the present invention to provide a mooring system and method and system for accommodating a large relative vertical movement of a ship when docked which overcomes the problems of the prior art.
A still further object of the present invention is the provision of a seal for use in an attachment element for use on a mooring robot.
It is an object of the present invention to address the foregoing problems or at least to provide the public with a useful choice.
Further aspects and advantages of the present invention will become apparent from the ensuing description which is given by way of example only.